In the prior art, the halftone rendering methods most commonly used are the error-diffusion or threshold matrix methods.
Threshold matrices may be dispersed or grouped or they may be a blue noise mask. The methods based on the matrices perform well in terms of processing speed but suffer from the appearance of regular structures.
The error-diffusion method suffers from the appearance of structure artifacts, especially waves. Waves characterize artifacts linked to repetitive structures, especially those obtained by the matrices. Structure artifacts take the form of changes in shape that are apparently irregular though visible to the naked eye. This can be resolved by implementing a trip of the image in serpentine mode, corresponding to a change in direction of the processing of the image at each row of the image. The term “round trip” of the image is also used.
Furthermore, in the image-processing systems of embedded printing circuits, the block processing of an image is the most optimized mode, especially for making specialized circuits. Now block processing of this kind adapts poorly to error diffusion algorithms because of the use of the serpentine mode. Chang and Allebach have proposed a block-screening algorithm, but this algorithm is complex to implement and calls for lengthy setting phases and a great deal of know-how to give good results.